Method of manufacturing synthetic sutures and the like



Patented Feb. 15, 1949 METHOD OF MANUFACTURING SYNTHETIC SUTURES AND THELIKE John P. Hollihan, Jr., Garden City, at, assignor to AmericanViscose Corporation, Wilmington, Del., a corporation of Delaware NoDrawing. Application January 17, 1946, Serial No. 641,865

This invention relates to improvements in methods for manufacturingsynthetic suture material and similar products comprising an integralmass of fibers which occur in animal parts, as for instance, animaltendons or sinews, such as beef tendons.

One method of producing filaments or threads comprising such animalfibers involves the steps of suspending the fibers, whether in theirelementary condition or after cutting thereof to selectively controlledlengths, as describedin the pending application of Hall, Hollihan'andMorehead, Serial No. 630,686, filed November 24, 1945, in an organic orinorganic acid, extruding the suspension into a coagulating and/ordehydrating medium, raising the pH on the thus formed filaments bytreating them in an aqueous bufier ing system and thereafter drying thebuffered filaments simultaneously with stretching thereof.

Stretching of the buffered filaments concomitantly with their drying isan essential step of the process, and I have found that in order toobtain final filaments or threads having the most desirable propertiesas respects tenacity and. extensibility, it is necessary to stretch thefilaments about 14 to 16% during the drying step, which is equivalent tosubjecting the filament bundle to a tensioning load which varies inaccordance with the size of the filament, from about 70 gms. for a 200denier filament to about 200 to 250 gms. for a 1000 denier filament, asmeasured by any standard strength-testing device. I have discovered,further, that in order to produce filaments capable of accepting therequired stretch during drying without rupture at the weaker portionswhich inevitably occur along the filament length, it is important toavoid excessive swelling of the filaments when the pH on the acidicfilaments is raised by treating them with a bufiering solution. Thus,excessive swelling of the filaments in the bufier system has been foundto reduce the capacity of the filaments to withstand, at all portionsalong their length, the stresses and strains developed therein when theyare stretched during drying,

Theacidic filaments invariably swell when they are subjected to theaction of alkaline solutions, but I have found that if the extent of theswelling is controlled so that the buffered filaments are swollen toabout twice their normal (dry) size, the filaments accept a stretch of14 to 16% during drying without rupture, and the final filaments arecharacterized by high tensile strengths andextensibilities. 1 I

Li The object of thepresent invention thereiore,

5 Claims. (CI. 1854) is to provide a method for raising the pH on theacidic filaments while controlling the extent of swelling of. thefilaments during bufiering thereof.

This and other objects are achieved by treating the acidic filamentswith an aqueous alkaline solution which, under the conditions oftreatment, has a limited swelling action on the filaments such that thebuffered filaments .are swollen to. only about twice their normal (dry)size after withdrawal thereof from thebufiering medium.

One buffer system which has been suggested for use in treating theacidic filaments comprises an aqueous solution of ammonium hydroxide andammonium chloride. It has been found that all solutions of ammoniumhydroxide and ammonium chloride are not satisfactory for use in treatingthe acidic filaments from the point of view of controlled swelling ofthe filaments and ability of the buffered filaments to withstandstretching. tow the required 14 to 16% without rupture duririgidryingthereof. I 'havefou'nd that both dilute and highly concentrated solutions of the ammonium compounds have a pronounced swelling action on thefilaments and that the filaments thus swollen have a markedly decreasedcapacity to undergo stretching without rupture. I have discovered,however, that-there is an optimum concentration of the ammoniumhydroxide and ammonium chloride in the buffering solutions at which thepH on the filaments is raised while at the same time the filaments areswollen only to a minimum controlled extent which does not prevent theiraccepting a stretch of about 14 to 16% without rupture. Thus I havedetermined that when the dry acidic filaments are immersed in water towhichhas been added about 6 to 6.5 cc. of concentrated am moniumhydroxide and about 1 to 1.2 grams of ammonium chloride, per liter, forabout eight minutes the filaments leaving the buffering medium areswollen to a size which is only about twice their normal (dry) size. Theterm concentrated ammonium hydroxide is used here in its usual sense todefine an aqueous solution containing approximately 28% NH; by'weightand of sp. gr. 0.90, (Handbook of Chemistry, Lange, p. 1165, 1944;Talbots Quantitative Chemical Analysis, 1939, p. 284; QualitativeChemical Analysis, Prescott and Johnson, p. 618)". In contrastto, thiscomparatively slight swelling of the filaments when they are buffered inaqueous; media containing the amm nium like, which comprises suspendingthe fibers in an aqueous acid solution, extruding the suspension into anon-basic coagulating and dehydrating medium to form acidic filaments,withdrawing and drying the thus formed acidic filaments and raising thepH on the filaments while swelling the fibers to approximately twicetheir normal dry size by treating them with water to which has beenadded about 6.3 cc. of concentrated ammonium hydroxide and about 1.07grams of ammonium chloride, per liter, and thereafter drying thefilaments while stretching them from 14 to 16%.

3. Method for the manufacture of threads and the like comprising anintegral mass of fibers which occur in animal sinews, tendons, and thelike, which comprises suspending the fibers in an aqueous acidsolutionfextruding the suspension into a non-basic coagulating anddehydrating medium consisting of an organic solvent, to form acidicfilaments, withdrawing and drying the thus formed acidic filaments andraising the pH on the filaments, while swelling the filaments toapproximately twice their normal dry size, by treating them with waterto which has been added from about 6 to 6.5 cc. of concen-.

trated ammonium hydroxide and from about 1 to 1.2 grams of ammoniumchloride, per liter, and thereafter drying the filaments whilestretching them from about 14 to 16%.

4. Method for the manufacture of threads and the like comprising anintegral mass of fibers which occur in animal sinews, tendons, and thelike, which comprises suspending the-fibers in an aqueous acid solution,extruding the suspension into a non-basic coagulating and dehydratingmedium consisting of acetone to form acidic filaments, withdrawing anddrying the thus formed acidic filaments and raising the pH on thefilaments, while swelling the filaments to approximately twice theirnormal dry size, by treating them with water to which has been addedfrom about 6 to 6.5 cc. of concentrated ammonium hydroxide and fromabout 1 to 1.2 grams of ammonium chloride, per liter, and thereafterdrying the filaments while stretching them from about 14 to 16%.

5. Method for the manufacture of threads and the like comprising anintegral mass of fibers which occur in animal sinews, tendons, and thelike, which comprises suspending the fibers in an aqueous acid solution,extruding thesuspension into a non-basic coagulating and dehydratingmedium consisting of acetone to form acidic filaments, withdrawing anddrying'the thus formed acidic filaments and raising the pH on thefilaments, while swelling the filaments to approximately twice theirnormal dry size, by treating them with Water to which has been addedabout 6.3 cc. of concentrated ammonium hydroxide and about 1.07 grams ofammonium chloride, per liter, and thereafter drying the filaments whilestretching them from about 14. to 16%. 1

JOHN P. HOLLIHAN, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS FOREIGN PATENTS Country 7 Date Great Britain May28, 1931 Great Britain Apr. 1, 1938 Number Number

